Telecommunication system with video and audio frames

ABSTRACT

An interactive system transfers video and audio information from a central facility to terminals by means of addressed television frames. Each audio frame includes information representing a single channel of time compressed audio. The terminals store correctly addressed frames. Video frames are repeatedly replayed to provide series of still-frame images. The audio frame is used to generate a normal speed audio output.

RELATED APPLICATIONS

The following applications filed simultaneously with this applicationpertain to different features of the telecommunication system describedherein.

Ser. No. 044,388, filed Apr. 30, 1987 Telecommunication System WithBurst and Continuous Audio Signals discusses attenuating a continuousbackground channel when burst audio is played.

Ser. No. 044,394, filed Apr. 30, 1987 Telecommunication System WithSelectable Audio Channels describes a system having two or morecontinuous audio signals sent on a first transmission medium andselected in response to a signal sent on a second transmission medium.

Ser. No. 044,387, filed Apr. 30, 1987 System for Synchronizing DigitalBit Stream for Telecommunication System discloses use of data clockpulses derived from color burst to sync data with flag bit.

Ser. No. 044,395, filed Apr. 30, 1987 Telecommunication System WithFrame Selected Continuous Audio Signals describes a system having framedaudio and two or more continuous audio channels which are selected inresponse to a control signal.

INCORPORATION BY REFERENCE

U.S. Pat. No. 3,746,780 is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention pertains to telecommunications and, more particularly, isconcerned with interactive telecommunication systems.

A number of telecommunication systems have been suggested and deployedwhich allow a terminal user to request particular video information froma remote repository. Services possible with such systems include, butare not limited to, information searches, retrievals, financialtransactions, reservations, and shopping.

With some systems, both the user requests and the video information aresent on a single duplex medium such as telephone lines. Examples of suchsingle medium systems are described in U.S. Pat. Nos. 4,500,751 and4,578,535.

In other systems, requests are sent over telephone lines and the videoinformation is sent over a broader bandwidth medium, such as cable.Examples of such dual media systems are the subjects of U.S. Pat. Nos.3,746,780 and 4,616,263, and described in I² -Elektrotechniek/Elektronica No. 4-1986, pp. 35-39.

With the system of the aforecited U.S. Pat. No. 3,746,780, a userwanting a service telephones a code number to a central facility. At thecentral facility, the selected video information is recovered from videodiscs or other storage means and sent as still television frames to theuser over cable or other media. As many terminals are usually coupled tothe same medium, each still frame contains a location number or addresswhich is read by address detectors located at the terminals. Only thoseframes with the same address as the terminal are accepted. An acceptedframe may be digitally stored by the terminal and repetitively displayedon a conventional television receiver.

Examples of video information include menus, forms, data, text, andstill pictures. It is desirable but lacking in the described system tohave audio information such as music and voice accompany the video.

In a publication dated May 1978, NHK (the Japan BroadcastingCorporation) a system is described for sending still pictures withaccompanying program sound. Frames for a number of programs are timemultiplexed. Each video frame has a code identifying the program towhich it belongs. The sound signals of all the programs are digitallyencoded and time divisionally multiplexed on lines within an audioframe. Both the video and audio frames are in the standard NTSC format.The video frames are sent serially with each video frame followed by twoaudio frames. Each video frame carries analog video informationcorresponding to one program, while each audio frame carries digitizedaudio information corresponding to all programs.

A receiver seizes and records video frames of a selected program forrepetitive display. The analog video may be digitized and stored in asolid state memory while apparently the audio is converted to analog andplayed as received. The NHK system is appropriate for broadcasting aplurality of predetermined programs, but it is not optimal forinteractive broadband services where many users can initiate andinteract with programs or services at different times.

SUMMARY OF THE INVENTION

Briefly, a telecommunication system transmits both video and audioinformation in frames. Each audio frame contain information representinga single channel of time-compressed bursts of audio. The frames are senton a transmission medium from a facility to a terminal which detects theframes and determines whether they contain audio or video information.Video information is stored at the terminal and repeatedly displayed asa still image. Audio information is stored at the terminal and played atnormal speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a telecommunication system embodyingthe system;

FIG. 2 shows in more detail a video server subsystem of the CentralFacility seen in FIG. 1;

FIG. 3 represents video and audio frames used to carry information fromthe Central Facility to Terminal;

FIG. 4 illustrates waveforms on a bit synchronization system; and

FIG. 5 is a block diagram of a Terminal used in the system of FIG. 1.

DESCRIPTION OF INVENTION

A telecommunication system 10 embodying the invention is shown inFIG. 1. A Central Facility 11 is coupled to a plurality of terminals 12through a first transmission medium 13 having a bandwidth sufficient tocarry standard television frames. First transmission medium 13 may becable, such as a CATV network. Optical fiber, air, and other widebandmedia are also suitable. The Central Facility 11 and terminals 12 arealso coupled by a second transmission medium 14 allowing duplextransmission of control signals not requiring a large bandwidth. Thelocal switched telephone system is a satisfactory second transmissionmedium, allowing low bit rate signals to be sent between the facilityand a specific terminal. Alternatively, the low bit rate signals can betransmitted over the aforementioned broadband medium 13.

Central Facility 11 provides both video and audio information inresponse to subscribers' requests. The video information representsstill frames of text, pictures, or other images sent as a series ofaddressed video frames. Each still frame may be displayed for severalseconds on a television set or monitor connected to the terminal, duringwhich time it is desirable to provide audio to accompany the video.

The system preferably has two types of audio: continuous and specific,both of which may be played simultaneously. Continuous audio is sent ona real time basis on, for example, audio channels. An example ofcontinuous audio is background music. Specific audio is so calledbecause it is specific to the displayed still frame. Typical specificaudio is voiced narrative or instructions. Specific audio is intendedfor only certain selected terminals at a time and is sent intime-compressed bursts by addressed frames having the same address asthe accompanying video frame. Only one channel of time-compressed audiois carried in an audio frame.

Both audio frames and video frames are in the same television format,such as the NTSC system. The same principle is directly applicable toother television systems like PAL or SECAM.

In the NTSC system, each frame is 1/30 second long and consists of twofields with 262.5 horizontal lines each. The lines of two fields areinterlaced for a total of 525 lines per frame. Approximately 21 linesoccur during a period called the vertical blanking interval (VBI) whichis at least 1.33 mS long. These lines do not appear on the televisionscreen, leaving about 483 lines of video in a frame.

The NTSC system is described briefly in "Federal CommunicationCommission, Public Notices" of Dec. 17, 1953 and June 6, 1954.

When the NTSC standard was written, a minimum VBI of 1.33 mS wasnecessary to allow the scan to return to the top of the picture tubebetween fields. Schemes for sending auxiliary information during one ormore lines of VBI have been developed such as described in U.S. Pat. No.3,493,674 and in North American Broadcast Teletext,Specification-Engineering and Development Department, CBS Television,Newark, N.J., June 22, 1981.

In the present invention, addresses, mode codes and errordetection/correction are sent on one or more lines (e.g., line 12)during the VBI of both video frames and audio frames. The address alertsan addressed terminal that a correspondingly addressed frame is to beaccepted. The mode code identifies the frame as either video or audio,and its sequence with other frames so that the terminal can process itaccordingly.

The audio frame information, which may be digital or analog, is sent intime-compressed bursts, allowing one or more seconds of audio to becarried by each 1/30 second frame. The terminal stores thetime-compressed audio frame and plays it at normal speed through atelevision receiver.

The Central Facility 11 consists of four basic subsystems: aConcentrator Subsystem 15, a Server Subsystem 16, a Video Subsystem 17,and Control and Maintenance Subsystem 18.

Each of the subsystems may be implemented on a commercially availablegeneral purpose computer, with the interconnections being provided by aLocal Area Network (LAN) 19. The software of each of these subsystemsmay be designed as a self-contained entity, with the inter-subsysteminterfaces conforming to a standard inter-processor protocol. Thisallows for a complete Central Facility system configuration where eachsubsystem consists of a separate processor or group of processors.However, in smaller configurations, one or more of these subsystems maybe implemented on a single computer while still maintaining the softwareinterfaces that allows simple expansion to multi-computerconfigurations.

The Control and Maintenance Subsystem 18 provides the administration forthe Central Facility 11 and is also responsible for the gathering ofstatistics on the workings of the overall system. The Control andMaintenance Subsystem 18 is not necessary to practice the presentinvention and will not be discussed further.

The Concentrator Subsystem 15 is the interface to the terminals for allcontrol and communication purposes. It is accessed by a remote terminalon the second transmission medium 14 which may be a dial-up connectionthrough the public telephone network, or an RS232C direct terminalaccess interface for high usage control terminal activities.

The Server Subsystem 16 acts as the overall controller of a sessionusing input from the Terminal 12, via the Concentrator Subsystem 15, toaccess the appropriate databases and to send instructions back to theConcentrator Subsystem 15 as to which video and audio frames to send tothe user.

The Video Subsystem 17 which is seen separately in FIG. 2 stores andsends to the terminals 12 via the CATV link 13 video and encoded audioinformation frames. Video still frames are stored in optical Video DiskUnits 20 in standard NTSC composite baseband format. About 54000 stillframes can be stored on each disc.

Since the seek time of the video disc units is longer than desired, manymore than the minimum number of video disc units to accommodate all thestill frames is needed. The video disc units 20 provide ac coupledsignals, so a dc restorer 21 is needed to precede a non-blocking videomatrix switch 22.

If the user calls for a video still frame, a central processor 23identifies its location on an available video disc unit. After the unithas reached the requested still frame, it advises switch 22 which thenswitches one frame into a pulse insertion device 24. The pulses insertedcome directly from the station sync master. The frame is then connectedinto a channel processor 25 which inserts addressing, mode code anderror codes on a VBI line. The addressed frame is connected into thevideo input of a CATV modulator 26.

Audio frames (of which more than one may be associated with a particularvideo frame) are previously digitally stored on Winchester-type magneticdiscs 27 in a 8-bit PCM encoded format at a sampling rate of 16 KHz forexample. A disc drive unit which can accommodate about 1 Gbyte willaccommodate about 1000 minutes of audio at 124 kb/s.

It is also possible to store time-compressed audio in analog format tobe transmitted as an analog signal.

In order to store as much audio as possible on each frame, the audio iscompressed. One or more seconds of real time audio are sent on each 1/30second frame, depending upon the type of compression.

Central processor 23 identifies those audio frames to accompany aselected video frame and unloads them from the correct addresses in aWinchester disc 27 into a buffer memory 28. After the transfer has beencompleted, the Central processor 23 calls for a corresponding number ofblack frames via the switch to accommodate the audio data. These blackframes include color bursts for clock recovery in the terminal. Eachactive line is at black level. In the NTSC system, black is representedby a low signal level. The data is inserted by the channel processor 25.The data bits are converted to pulses which are first conditioned by aNyquist filter to reduce inter-symbol interference, as well as toprevent interference on the sound channel and the spreading of energy onadjacent channels before they are summed onto the black frame raster.

A transmission bit rate of 8/5 of the color subcarrier frequency3.579545 MHz (5.727272 Mb/sec) may be used. The data clock has a periodof 174.6 nanoseconds. While this is the same bit rate as Teletext, whichis approximately the fastest bit rate which can be carried by most CATVsystems, the preferred formatting of the data and the method of clockingthe incoming data are much more efficient and significantly different.

Turning briefly to FIG. 4, on each line on which there is data, a flagbit in the form of a "1" bit is placed, for example, 10.5 microseconds(60 data clock pulses) after the leading edge of the horizontalsynchronization pulse. It is then followed by 288 bits (i.e., 36 bytes)of data. For the audio data, this results in total of 142272 bits/frame.

Referring to FIG. 3 in both audio and video frames four lines within thevertical blanking interval are reserved for addressing and mode (videoor audio) and error codes, and future use. In audio frames, line 16 toline 262 on field one and line 279 to line 525 on field two are used forthe audio data.

Referring again to FIG. 2, the black frame with the audio data isswitched for the period of one frame (approx. 1/30 second) into thevideo input of a CATV modulator 26. The video frames are also passed onto the video input of the CATV channel modulator 26. There is always acontinuous stream of still frames with black burst frames being switchedin when no information frames are delivered. Each channel modulator isselected for transmission through a single coaxial distribution systemand a single coaxial cable system 13. With a set of projected trafficpatterns, there might typically be over 100 active users sharing onechannel. Video and audio frames of a program are time multiplexed withothers on a CATV video channel and sent to remote terminals. Continuousaudio is sent on an audio channel.

Central Facility 11 employs the BTSC multichannel television soundformat to place continuous audio (e.g., background music) in up to threeseparate audio channels 30 in the NTSC composite signal. A SAP (secondaudio program) channel is used. Three possible channels are the monaural(left plus right), the stereo difference channel, and the SAP channels.It is also possible to make available many more distinctly differentbackground music channels to the user.

Both the continuous audio and the framed specific audio described abovemay occur simultaneously. When the video specific audio is played out inreal time at the user terminal, the background component, if present, isattenuated automatically. The central processor 23 controls theselection of the background channel (or silence) at the user's terminaleither through control signals inserted by the channel processor 25 intoline 12 of the vertical blanking interval or by control signals sentover the telephone loop 14 by Concentration Subsystem 15. The user mayalso have the capability of muting it. The continuous audio sources areconnected into the audio input of the same modulator 26.

The audio inputs of the channel modulators 26 can be driven either fromindividual SAP channel encoders 31 or can all be driven from a singleencoder using a suitable distribution unit 32.

The video and audio frames, as well as the continuous audio, aredistributed through the CATV network 13 to the terminals.

Turning now to FIG. 5, a terminal, 12 consists of a set-top module,enclosed by dashed lines in the drawing and a remote keypad 34.

A connector panel (not shown) on the set-top module provides variousphysical connectors, including:

Cable in -- 75 ohm coaxial F-connector

TV out -- 75 ohm coaxial F-connector

Telephone line -- RJ-11 telephone jack

Auxiliary phone -- RJ-11 telephone jack.

Through these connectors, the terminal 12 is coupled to a CATV channel13, telephone loop 14 and a television receiver or monitor 35.

Set-top module contains hardware and software for data communications toand from the Central Facility 11 and for receiving and processing videoframes and audio frames sent from the Central Facility and deliveringthem to the television receiver 35. The set-top module also contains apower supply, and a controllable modem 36 as the interface to thetelephone loop 14.

CATV tuner demodulator 38 receives a selected NTSC channel signal overthe CATV network. This composite signal contains video frames, digitallyencoded audio frames, and BTSC encoded audio channels. CATV tunerdemodulator 38 demodulates the incoming signal to baseband and splitsthe audio channels from the video and audio frames.

The audio channels extracted from the audio output of CATV tunerdemodulator 38 are separated by a low-pass filter 39 and a SAP channeldecoder 40. They are connected into an analog switch 41, which iscontrolled by a control signal from the Central Facility 11 sent on thevertical blanking interval, or alternatively through the telephone loop14 to select baseband audio or SAP audio. Preferably, however, aselection code stripped from a frame controls switch 41 to select thedesired continuous audio signal. A locally generated "mute" commandoverrides the control signal. The selected channel is passed through aswitched attenuator 42 (e.g., 12 dB) which is switched in automaticallyby a signal generated by audio control 43 when audio is being playedfrom the alternate audio-frame source (i.e., audio specifically toaccompany the display). This is so that the background audio, e.g.,music, does not obscure the video specific audio channel, e.g., voice.The output of the attenuator is then connected to a summer 44 which addsthe analog signal derived from the audio frame, which is then connectedinto the audio input of a channel of modulator 45 which couples it totelevision set 35 for playing.

In response to pressing a mute key on keypad 34, a signal from IRreceiver 65 causes the CPU 67 to activate one of the two control lineson the muart 37, labelled F. This in turn opens a switch disconnectingthe continuous audio from the output of switch 41. This results in thecontinuous audio to be disconnected from attennuator 42 thereby mutingit. Pressing the mute key once more deactivates the control signal toswitch 41 which results in unmuting of the continuous audio. Muart 37,which may be an Intel 8256 Multifunction Universal Asynchronous ReceiverTransmitter LSI, provides the serial I/O interface to the modem 36. Inaddition, two of the parallel lines labelled F are used to control themute and background audio select switches in the switch block 41. Theselected channel out of switch 41 is applied to attenuator 42.

Each video and encoded audio frame received from the Central Facility 11had been tagged with a three-byte terminal address and a two-bit modecode and a background sound control code in line 12 of the VerticalBlanking Interval (VBI). A VBI correlation circuits 46, 47, 48 uses theaddress to decide whether the current frame belongs to the terminal, andthe command code to determine the handling of the frame. The mode codecan have one or four meanings:

Video frame;

Video frame; stop preceding audio

Audio playout; initial frame

Audio playout; continuation frame.

The vertical and horizontal drives are used to identify all frame linesby number. Line 12 is read out and the address and mode (video or audio)bits are connected over to the VBI processor 46, a mode/tag register 48and error detector 47. The address is correlated with the user addresswhich is resident in an address register 49, and then the mode bits arechecked to determine the type of frame, so that appropriate action canbe taken. Each frame transmitted from the Central Facility is taggedwith numbers that repeat in 64 blocks. These can be interrogated by theCentral Facility to check the delivery of any specific still framerecently transmitted.

If the address in line 12 correlates with the terminal ID, thendepending upon the mode (video or audio), the frame is inserted into theappropriate store. In the case of audio, they are stored in bursts(line-by-line) of 5.7272 Mb/s and clocked into audio RAM 50,line-by-line through the appropriate set of frames.

After the audio data segment has been received, it is played out fromthe RAM 50 at the appropriate speed (e.g., 128 kb/s) through D/Aconverter 51 which includes a 7.5 KHz low pass filter. The analog outputfrom the D/A converter is passed to the sound summer 44 which connectsinto the audio input of the channel 3 modulator 45. It is summed withthe selected continuous audio channel which is attenuated until thesequence is completed.

The frames from demodulator 38 are connected, via a dc restorer 52, to acolor subcarrier (3.58 MHz) band-pass filter 53. Its output is passed onto a color-subcarrier regenerator chip 54. For this to operate, it isnecessary for it to be provided with a burst flag gate. To achieve this,the synchronization pulses are stripped off the incoming video frames bysync stripper 55 and connected into a synchronization pulse generator56. The outputs from generator 56 include horizontal drive, verticaldrive, and color subcarrier burst flag. All clocking frequencies forsynchronization are derived from the color subcarrier bursts alwayspresent on the incoming still frames. For sync generator 56 to operate,it needs an input of four times the color subcarrier frequency (14.32MHz). This is provided by a phase-locked loop 57. The output of theregenerated color subcarrier frequency is connected into thephase-locked loop which locks in a 8 times color subcarrier oscillatorfrom which the 4 times color subcarrier is derived.

The dc restored frames from DC restorer 52 are connected to a bufferwhich generates TTL logic levels from the bits on the raster. These areconnected into the clock generator and data extraction circuit 59. Thisdata extraction makes efficient use of the raster frames.

The leading edges of the horizontal synchronization pulses slope toomuch to accurately synchronize the bit train. Accordingly, a bitsynchronization circuit is used. It will be recalled that the first biton each data line is a "1," placed 10.5 microseconds (60 data clockpulses after the leading edge of the horizontal sync pulse. This iscalled a flag bit. The 8 times color subcarrier source is connected toclock 59 which divides by 5 to derive 174.6 nanosecond data clockpulses. The leading edges of the horizontal synchronization pulses areused to start a count using the data clock 59. Turning now to FIG. 4after a count of 58 data clock pulses (10.127 microseconds) a gate ortime window is opened for the 8 times color subcarrier clock (28.64 MHz)for a period of 5 data clock pulses (873 ns). These 5 data clock pulsesare "and"ed with the data bit stream so that when the leading "1" (e.g.,flag bit) is present, its position with respect to the five data clockpulses, is identified and is used to correctly synchronize the dataclock to the rest of the data on the line.

Returning now to FIG. 5, a flash A/D converter 60A, part of video coder60, clocked at about 14.32 million 8-bit samples per second, continuallyprovides data into input register 61, but it is not transferred intomemory bank 62 (3.82 Mb) until a strobe is received. If the moderegister 48 recognizes the incoming frame as being addressed to the userterminal and being for video display a strobe is sent to the video framestore. The memory bank 62 is then loaded from register 61 for the periodof exactly one frame (approx. 1/30 second.) It is then played out asstill frame through D/A converter 60B repetitively using the 4 timescolor subcarrier clock (14.32 MHz). Since there is a color subcarrierphase jump between every other frame, this is corrected in the framejump correction block 63.

Before being connected into the video input of the modulator 45, thevideo signal is passed through a character generator 64. This is used toinsert characters as they are entered from the user keypad 34. They aretypically inserted close to the bottom of the screen display.

The system provides interactive data retrieval and transaction. Theinfra-red keypad 34 provided with the system is equipped with anadequate number of keys (e.g., 53) to interact with the system,including alpha-numeric and various special function keys to providesimplified, dedicated operation of on/off, page forward, page back,pause, purchase and other functions.

The keypad 46 transmits PCM-encoded IR commands to the set-top modulevia an infra-red receiver 65. The keypad is the mechanism for the userto control the set-top module and to communicate with the CentralFacility 11 via the telephone loop 14. The keys are used to control theterminal, Central Facility functions, as well as to input transactionspecific data by the users.

IR receiver 65 includes a decoder to convert the special encoded IRpulses into a convenient form for inserting onto the 8085 CPU bus 66.

Data communications with the Central Facility 11 may be provided bymodem 36 that transfers asynchronous ASCII data at a rate of 300 or 1200bps via a telephone switching office. Modem 36 has autodial capabilityfor automatic placement of calls to the Central Facility. LED indicator74 is a data carrier detector.

The terminal is controlled by microprocessor 67 coupled to system bus66. A 8085 CPU may be used. MUART 36 is connected to system bus 66.

Decoder interface 68 is used as a buffer between the bus 66 and thecircuits associated with the line 12 data. Address decoder 69 is adaptedto the 8085 bus 66. The program firmware is stored in EPROM 70. EEPROM71 is used to store information from Central Facility 11 via thetelephone connection 14. Examples of these are the terminal address,passwords, and display characters used before a connection isestablished.

EEPROM 71 also provides storage of banners and messages for display, andalso terminal identification (serial number) and terminal type (versionnumber) for use in the Log-on process. Messages that are stored inEEPROM include the following:

Call being placed

Call completed

Call attempt failure

Video channel failure

IVS session ended

Call disconnected.

Data for these prestored messages can also be downloaded to the terminalover the telephone loop 14 from the Central Facility 11.

Terminal 12 has the capability to receive ASCII text over the telephoneline 14 or retrieve it from the EEPROM and switch it onto the videoframe currently being displayed. A blank frame generated by syncgenerator 56 allows display of only the ASCII text. The video charactergenerator 64 produces characters for display on the screen.

When the terminal is in the "off" state, only the infra-red receiver ispowered. In this state, the set-top module is totally transparent to theTV signal. This transparency is provided by a switch 73 that connectsincoming signals to the television set 35 with all set-top modulecomponents disconnected.

When the Terminal 12 is turned on, the locally stored banner isdisplayed on the screen and the terminal modem auto-dials the CentralFacility 11. When the Concentrator Subsystem 15 detects the power-upmessage (which is sent by the Terminal 12 once carrier is detected onthe telephone loop 14), it sends a prompt to the Terminal 12 to transmitits identification number. The Concentrator Subsystem 15 then sends amessage to the Server to establish a new session.

In one mode of operation, in order to control service use bysubscription only, the Server Subsystem 16 sends a log-on form to theterminal 12, and the user ID and Password keyed in by the subscriber areverified against the database. Should the user ID or Password beinvalid, the appropriate error message is sent by the Server Subsystem16. The user is allowed two input errors but if there is still an erroron the third attempt, the session is terminated by the Server Subsystem16 on the assumption that the access is being attempted by anunauthorized user. The carrier signal on the telephone loop 14 isdropped and the Terminal 12 becomes disconnected from the system. Whenvalid ID and Password have been received by the Server Subsystem 16, aconfirmation message is sent to the Concentrator Subsystem 15, which inturn sends a "session start-up" message to the Video Subsystem 17.

As part of the subscriber profile in the Server Subsystem database,there is the CATV channel number to which the terminal is tuned and thisinformation is passed to the Video Subsystem 17 as part of the "sessionstart-up" message. The Video Subsystem 17 selects the initial videoframe (with associated audio frames as required) from storage asinstructed by the Server System 16. The Video Subsystem 17 selects anavailable time slot on the appropriate channel and sends the selectedframe(s) each with the terminal address encoded in line 12 of the VBI. A"start-up response" message is sent from the Video Subsystem to theConcentrator to complete the log-on procedure.

After viewing the initial screen (e.g., a main menu), the Terminal userindicates his next request via one or more keystrokes on the remotekeypad. These keystrokes are transmitted over the telephone loop 14 andinterpreted by the Concentrator Subsystem 15. The Concentrator System 15then generates and sends to the Server Subsystem 16 a Video/AudioProcessing (VAP) message. The Server Subsystem 16 uses this informationto search its database to find the identities of the information framesthat will satisfy the subscriber's request. This information is returnedto the Concentrator Subsystem 15 in a two-part message. The first part,called the Page Control Record, contains information pertaining to anyprompt or cursor controls that must be sent to Terminal 12 via telephoneloop 14. This information is retained by the Concentrator Subsystem 15.The second part, called the Page Display Record, contains informationconcerning the frames to be sent (single frame or timed sequence,identities of all video and audio frames), and this is passed on to theVideo Subsystem 17. The Video Subsystem 17 uses the PDR to access theVideo Subsystem database and retrieve the requested frames from storage.The frames are then transmitted in sequence to the terminal during aselected available time slot via the CATV link 13.

Processing of the subscriber's requests continues in the mannerdescribed above until a log-off message is received by the ConcentratorSubsystem 15 which in response sends a disconnect message to both theServer Subsystem 16 and the Video Subsystem 17. The Video Subsystem 17sends appropriate information regarding the session to the Control andMaintenance Subsystem 18, and deallocates all data structures used inthe session.

The use of both a CATV (or equivalent distribution system) and atelephone loop 14 to interconnect the Central Facility 11 and theTerminal 12 allows the addition of more sophisticated interfaces withthe system. One such application is the inclusion of a Customer ServiceRepresentative (CSR). The subscriber who decides he needs someassistance while in the middle of a session can use either standardtelephone calling features or the services of the Concentrator Subsystem15 to put the connection "on hold" and make a telephone connection to aCSR. The CSR (through a second terminal) would then have the ability tocontrol the user's session, i.e., control what is sent to the terminal12, while talking to the user over the telephone loop 14. At the end ofthe consultation, the CSR would drop from the connection, returningcontrol to the user.

What is believed to be the preferred embodiment and best mode ofpracticing the invention has been described. Other embodiments andmodifications will, however, be apparent to those skilled in the art.Therefore, the scope of the invention is to be determined by the claims.

What is claimed is:
 1. A telecommunication system for transmitting stillvideo frames and accompanying audio over a first transmission mediumcomprising a facility and a terminal, wherein said facilityincludes:means for providing video frames, wherein each video frameincludes information representing an image; means for providing audioframes, wherein each audio frame includes information representing asingle channel of time-compressed burst of audio; means for inserting amode code into each of said video and audio frames signifying whetherthe frame is a video frame or an audio frame; and means for coupling aseries of video frames and audio frames to said transmission medium, andwherein said terminal includes: detecting means for detecting frames onsaid transmission medium; medium responsive to said mode code fordetermining whether said frames are video frames or audio frames; firststorage means for storing information included in a video frame; meansfor repeatedly displaying the image represented by information stored bysaid first storage means; second storage means for storing informationincluded in at least one audio frame; and means for providing in normaltime, an audio output signal corresponding to said information stored insaid second storage means.
 2. The telecommunication system of claim 1wherein each frame is addressed and said terminal is addressable.
 3. Thetelecommunication system of claim 1 wherein each frame includes avertical blanking interval and each mode code is a digital signal in thevertical blanking interval.
 4. The telecommunication system of claim 3wherein said mode code has at least two bits indicative of the contentsof each frame and how such contents are to be controlled.
 5. Thetelecommunication system of claim 3 wherein each mode code has two bitsand has one of the following meanings:video frame, video frame, stoppreceding audio; audio playout, initial frame; and audio playout,continuation frame.